2-Substituted -4,5-diamino-6-cyanopyrimidines

ABSTRACT

Certain novel, 4,5-diamino-6-cyanopyrimidines, e.g., 2,6dicyano-4,5-diaminopyrimidine and 2-alkoxy-4,5-diamino-6cyanopyrimidine, useful as epoxy curing agents, are prepared by the cyclization of certain 1-amino-2-(substituted)maleonitriles, prepared in turn from the reaction of diaminomaleonitrile and selected substituted cyanoformimidates.

United States Patent [19 Begland [4 May 13, 1975 Z-SUBSTITUTED [56] References Cited -4.S-DIAMiNO-fi-CYANOPYRIMIDINES UNITED STATES PATENTS [75] inventor: Robert W. Begiand, Wilmington. 2.139.870 12/1938 Wiirmmne et ul. 260/2564 Del. [73] Anignee: E. I. du Pont de Nemourl & Primary Examiner-Jame Company. Wilmington. Del. H7] ABSTRACT [22] Certain novel. 4.5-diamino--cyanopyrimidines. e.g., [2]] A l M 341,149 2.6-dicyano-4,5-diaminopyrimidine and 2-alkoxy-4,5-

diamino-fi-cyanopyrimidine, useful as epoxy curing u agents. are prepared by the cyclization of certain I- [52] So/256A 260/2 amino-Z-(substituted)maleonitriles, prepared in turn 51] lm Cl 260/465 from the reaction of diaininomaleonitrile and selected 58 Field of Search 260/2$6.4 c, 256.4 N amfmmmdnw 4 Chime, No Drawings Z-SUBSTITUTED -4,S-DIAMINO-6-CY ANOPYRI RIDINES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is concerned with. and has as its principal objects provision of, a process for the reaction of diaminomaleonitrile with cyanoformimidates and the successive novel substituted maleonitriles and isomeric pyrimidines that can be obtained therefrom.

2. Prior Art No direct references to the compounds or processes of this invention have been found. The closest art appears to be:

a. .1. Clark. et al., .1. Chem. Soc. 3221 (1964); 2-

et'noxy-4,5-diamino-6-ethoxycarbonylpyrimidine. b. S. Trofin ienko, et al., J. Org. Chem. 27, 433-8 (1962); 2-methy1-4,o-diamino-5-cyanopyrimidine.

c. Huber, .1. Am. Chem. Soc.. 65, 2226-6,( 1943); 2,-

4-diamino-5-cyanopyrimidine.

d. I-Iromatka, U.S. Pat. No. 2,235,638 (to Merck and Co., 1941);

INHZ NH H N HC 0 0-011,

caa-c-o-st v 0 I ,c /N 1iC cu NC c NR2 STATEMENT OF THE INVENTION There has now been discovered a process for reacting diaminomaleonitrile with an alkyl, alkoxyalkyl. arylalkyl, haloalkyl. or nitroalkyl cyanoforrnimidate, in a first step, to yield, respectively, a 1-amin0-2-(aminoalkoxymethyleneamino)-maleonitrile or 1-amino-2- (aminocyanomethyleneamino)maleonitrile. These latter compounds are cyclized, respectively. in a second step, to the corresponding 2-alkoxy-4,5-diamino-6- cyanopyrimidines or 4,5-diamino-2,6- dicyanopyrimidine.

The reactions may be represented by the equations:

III

R being a group of the formula I RCHR in which R and R alike or different, may be H. alkyl, alkoxy, alkenyl, alkynyl or alkoxyalkyl, all of up to 7 carbon atoms, or phenyl or any of their substituted derivatives having from ll4 (1 5 for phenyl) halogen (particularly fluoro or chloro) or nitro substituents and X is OR or CN.

When R has at least one B-carbon atom and said B-carbon carries at least two fluoro. chloro or nitro substituents. OR is a more active leaving group than cyano in the first reaction above and X in products 11 and 111 is CN.

When no B-carbon in R carries more than one fluoro. chloro or nitro substituent. OR is a less active leaving group than cyano in the first reaction above and X in products 11 and III is 0R R being defined the same as R above with the proviso that any a-carbon atom in R or R carries no more than one fluoro. chloro or nitro substituent.

The 1-amino-2-(substituted aminomethyleneamino)- maleonitriles of Formula 11 are crystalline solids which are useful for cyclizing into products of Formula 111. The 2-substituted-4.5-diamino-dcyanopyrimidines of Formula 111 are crystalline solids which are all useful as curing agents for epoxy resins, illustrated in Example A below.

Reaction of Diaminomaleonitrile with a Cyanoformimidate (Step 1) The reaction of diaminomaleonitrile with a cyanofor mimidate, as shown above, may be carried out neat since cyanoformimidates are liquids or can be reduced to liquids at mildly elevated temperatures. However, to provide for better control of the reaction and dissipation of the heat of reaction, it is preferred to employ an organic solvent which is inert to the reactants and products. Suitable solvents include ethers. such as tetrahydrofuran and dioxane; nitriles, such as acetonitrile and benzonitrile; chlorocarbons, such as methylene chloride, chloroform, carbon tetrachloride and tetrachloroethane; aromatic hydrocarbons. such as benzene and toluene, dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide, and the like. Alcohols, ketones and water tend to react with the starting materials and are to be avoided.

The reaction is catalyzed by the presence of acid. Any acid may be employed but a catalytic amount of a strong acid is preferred. Suitable acids include sulfuric acid, hydrochloric acid, trifluoroacetic acid, p-toluenesulfonic acid, oxalic acid. and the like.

Temperature and pressure are not critical parameters in the reaction. Temperatures from 0 to 200C and above are operable and temperatures in the range from 20 to about C are preferred. Pressures above and below atmospheric pressure are operable and atmospheric pressure is preferred for convenience.

The molecular proportions in which diaminomaleonitrile and the cyanoformimidate may be brought together to carry out this reaction may be varied widely, e.g.. from 1:20 to 20:], respectively. Proportions in the range from 2:1 to 1:2 are preferred and 1:1 proportions may be used to advantage.

Cyclization Reaction (Step 2) The cyclization (isomerization) of the l-amino-2- (substituted aminomethyleneamino)maleonitriles of Formula 11 to the 2-substituted-4,5-diamino-6- cyanopyrimidines of Formula 111 is catalyzed by a small amount of a strong base. Operable bases include trialkylamines, such as trimethyl amine and triethylamine; alkali metal alkoxides, such as sodium methoxide and sodium ethoxide; alkali metal hydroxides, such as sodium hydroxide and potassium hydroxide, and the like.

This base-catalyzed reaction may be carried out neat, eg. by melting the starting material in the presence of the catalyst. Howe er, it is preferred to employ an or ganic solvent which is inert to the starting material and product. Suitable solvents include ethers, such as tetrahydrofuran and dioxane; nitriles, such as acetonitrile and benzonitrile; chlorocarbons, such as methylene chloride, chloroform, carbon tetrachloride, and tetrachloroethane; aromatic hydrocarbons, such as benzene and toluene, dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide, and the like.

With compounds of Formula ll in which X is R the cyclization reaction may also be catalyzed by small amounts of strong acids in water, e.g., a catalytic amount of sulfuric acid, hydrochloric acid, trifluoroacetic acid, p-toluenesulfonic acid, oxalic acid, and the like, may be employed using water as the reaction medium.

Temperature and pressure are not critical parameters in the cyclization reaction. Temperatures from 0 to 200C and above are operable and temperatures from 20 to about 125C are preferred. Pressures above and below atmospheric pressure are operable and atmospheric pressure is preferred for convenience.

Products of Formulas 11 and Ill are isolated from the reaction mixtures in which they are formed by known means.

EMBODIMENTS OF THE lNVENTlON There follow some nonlimiting examples illustrating aspects of the invention. Examples 18 and the Table lis lose novel compounds of the invention. Example A is a utility example showing the use of the pyrimidines of the invention as epoxy curing agents. In these examples. parts are by weight unless otherwise specified.

EXAMPLE 1 1-Amino-2-(aminomethoxymethyleneamino )maleonitrile Part A A solution of 0.2 g of potassium cyanide in 16.0 g (0.50 mole) of methanol was cooled to C and about 26 g (0.5 mole) of cyanogen was bubbled into it over 0.5 hour. The resulting solution was warmed to room temperature and distilled to give 17.2 g (41%) of methyl cyanoformimidate, bp 7080C at 160 mm.

Part B To a solution of 4.20 g (0.05 mole) of methyl cyanoformimidate and 5.40 g (0.05 mole) of diarninomaleonitrile in 100 ml of acetonitrile was added 5 drops of concentrated sulfuric acid. The resulting solution was stirred for hours, filtered and stripped to give a yellow solid. Recrystallization from ether gave 4.98 g (60.6%) of l-amino-2- (aminomethoxymethyleneamino)maleonitrile as light yellow crystals, mp ll4l16C; IR (KBr) 2.89, 2.95, 2.99, 4.57, 6.02, 6.22 and 6.27 1.; UV (CH CN) 304 nm (5 15,000); NMR (acetone-d 3.60 8 (s, 3), 5.20 8 (b, 2), 5.75 8 (b, 2).

Anal. Calcd for C,,H,ON,,: C. 43.63; H, Found: C, 43.72; H,

EXAMPLE 2 l-Amino-2-(aminomethoxymethyleneamino)maleonitrile To a solution of 4.9 g (0.05 mole) of ethyl cyanoformimidate (L. Weinstock, et al., J. Org. Chem. 32, 282329, 1967) and 5.4 g (0.05 mole) of diarninomaleonitrile in 100 ml of acetonitrile was added 5 drops of concentrated sulfuric acid. After being stirred for 2 days, the solution was filtered, the solvent was removed by evaporation and the crude product was recrystallized from ether-petroleum ether to give 5.0 g (56%) of colorless crystals of l-amino-2- (aminomethoxymethyleneamino)maleonitrile, mp 108l 10C; IR (KBr) 2.88, 2.98, 4.48, 4.55, 6.05 and 6.25 11.; UV (CH CN) 305 nm (e 15,500); NMR (DMSO-d 1.20 5 (t, .l 7, 3), 4.18 5 (q, J 7, 2), 5.8 5 (b, 2). 65 8(1), 2).

was prepared from 1.0 mole of cyanogen and 1.0 mole of octafluoropentanol by the procedure of Example 1, Part A. There was obtained an 81% yield of the desired cyanoformimidate, bp 5860C at 0.50 mm. NMR (CDCI 478 8 (t, 2), 6.10 5 (t, 1), 9.50 8 (s, 1).

Anal. Calcd for C ILON F C, 29.59 H, 1.39; N, 9.85

Found: C, 29.75; H, 1.69; N, 10.03.

Part B To a solution of 34 g (0.12 mole of 2,2,3,3,4,4,5,5 octafluoropentyl cyanoformimidate and 10.8 g (0.10 mole) of diarninomaleonitrile in 200 ml of acetonitrile was added 10 drops of concentrated H The resulting solution was refluxed for 3 hours, treated with activated carbon and filtered, and the solvent was removed to give 15.5 g (97%) of l-amino-Z- (aminocyanomethyleneamino)maleofiitrile as a yellow powder. An analytically pure sample was obtained by recrystallization from chloroform-ethyl acetate as yellow crystals, mp l49-l52C (dec.); IR (KBr) 2.92, 3.02, 3.12, 4.46, 4.56, 6.09, 6.21 and 6.41 pa; UV (CH CN) 232 nm (e 5500), 288 nm (e 5800), 348

Anal. Calcd for C,,H,N.,: C. 45.00: H, 2.5 H. 2.5

N. Found: C. 45.19 N. 5

poo

EXAMPLE 4 l Amino-2-(aminocyanomethyleneamino)maleonitrile Part A 2,2,2-Trifluoroethyl cyanoformimidate was prepared in 95% yield from trifluoroethanol and cyanogen as a colorless liquid, bp 53C at 20 mm. IR (neat) 3.10, 3.20, 4.55, 5.95 and 6.0 [.L.

Part B A solution of 16.7 g (0.11 mole) of 2,2,2- trifluoroethyl cyanoformimidate, 10.8 g (0.10 mole) of diaminomaleonitrile, drops of concentrated sulfuric acid and 200 ml of tetrahydrofuran was stirred for 2 days at 25C. The resulting solution was filtered and the solvent was removed to give 15.7 g (98%) of l-amino- 2-(aminocyanomethyleneamino)maleonitrile.

E XAMPLE 5 1-Amino-2-( aminocyanomethyleneamino )maleonitrile Part A A solution of 74.7 g (0.5 mole) of trichloroethanol and 0.5 g of powdered potassium hydroxide in 50 ml of tetrahydrofuran was cooled to --20C and 26 g (0.5 mole) of cyanogen was bubbled in over minutes. The resulting solution was warmed to room temperature, the solvent was evaporated and 50 ml of ether was added to the resulting mixture of solid and oil. Filtration of this solution gave 11.2 g of colorless crystals. Evaporation of the ether gave 46 g (44%) of 2,2,2- trichloroethyl cyanoformimidate as a light yellow oil. 1R (nujol) 3.00, 4.45 and 5.95 4; NMR (CDCl;,) 5.0 5 (s, 2), 9.75 8 (b, 1).

Part B EXAMPLE 6 2,6-Dicyano-4,S-diaminopyrimidine A solution of 3.52 g of 1-amino-2- (aminocyanomethyleneamino)maleonitrile and 10 drops of triethylamine in 50 ml of acetonitrile was stirred at room temperature for hours during which time a yellow precipitate formed. Tetrahydrofuran (250 ml) was added and the resulting mixture heated to reflux and filtered to give 1.35 g (38%) of 2,6- dicyano-4,5diaminopyrimidine as a yellow powder, mp

(slowly darkens above 200C). The same product from a similar preparation gave the following analyses: IR (KBr) 2.91, 3.03. 3.19, 4.45, 6.07, 6.25 and 6.50 pt; UV (EtOH) 288 nm (e 7200), 325 nm (e 9700), 413 nm (e 4900). Evaporation of the tetrahydrofuran gave 1.0 g of 2,3diamino-5,fi-dicyanopyrazine.

EXAMPLE 7 2-Methoxy-4,5-diamino-6-cyanopyrimidine Part A Acid Catalyzed A slurry of 2.0 g of l-amino-2-(aminomethoxyme' thyleneamino )maleonitrile in 50 ml of water containing 1 drop of sulfuric acid was heated to reflux over 10 minutes. During this time the solid dissolved, the solution darkened in color and gold-brown needles began to form. The resulting mixture was cooled and filtered to give 1.66 g (83%) of 2-methoxy-4,5-diamino-6- cyanopyrimidine. Recrystallization from methanol or water gave dark gold needles, mp (slowly darkens above 180C). IR (KBr) 2.88, 2.94, 3.02, 3.05, 3.25, 4.50, 6.12, 6.20 and 6.52 t; UV (CH CN) 225 nm (e 7800), 306 nm (e 11,500), 378 nm (e 8500); NMR (DMSO-d.,) 3.09 8 (s, 3), 7.0 8 (b, 4).

Anal. Calcd. for C H ON C, 4 4.20; N, 4 .4 32; N, 4 .7

3.63; H, 1 Found: C. 44.02; H, 4. 6.

Part B Larger Scale Part C Base Catalyzed A solution of 19.0 g of l-amino-2-(aminomethoxymethyleneamino)maleonitrile, 4.5 ml of triethylamine and 400 ml of acetonitrile was stirred for 7 days at room temperature. Collection of the resulting precipitate gave 11.6 g (61%) of 2methoxy-4,5-diamino-6- cyanopyrimidine as a yellow-green powder.

EXAMPLE 8 2-Ethoxy-4,5-diamino-o-cyanopyrimidine Part A A slurry of 7.7 g of 1-amino-2-(aminoethoxymethyleneamino)maleonitrile in 250 ml of water containing 8 drops of sulfuric acid was heated to reflux and held there for 5 minutes. The resulting mixture was cooled and filtered to give 6.0 g (78%) of 2-ethoxy-4,5- diamino-6-cyanopyrimidine as gold needles. Recrystallization from ethyl acetate gave yellow crystals, mp l78C (dec.). The same product from a similar preparation gave the following analyses: IR (nujol) 2.85, 2.90, 3.03, 3.20, 4.50, 5.95, 6.10, 6.20 and 6.55 1.; UV (CH CN) 225 nm (e 8800), 306 nm (e 12,400), 379 nm (e 9200); NMR (DMSO-d,,) 128 8 (t, .l 7, 3), 4.32 8 (q, .I 7,2), 7.0 8 (b, 4); Mass Spec. 179 (M*), 134 (M*()Et).

Anal. Calcd for C H ON C. 46.92; H. 506; N. 39.09

Found: C147, H 5,l4; N, 38.9l.

Part B Base Catalyzed and -CH CH -OCH CH CH- CH -OCH CH CH(CH CH CH- CHCi-CH CH CH Cl, CH CH F, -CH(CH )-CH NO are substituted for ethyl cyanoformimidate in the procedure of Example 2, the respective substituted maleonitriles shown in the table which follows are obtained. These in turn are cyclized by the procedure of Example 8. Part A, to yield the respective 2-alkoxy-4,5-diamino-6-cyanopyrimidines shown in the Table:

TABLE item Product of Formula II Product of Formula III I i-Amino-2(aminoallylox 2-AllyloXy-4,5-diamino-6- ymethyleneamino )maleonicyanopyrimidine trilc 2 l-Ammo'2-|amino-( 2- 2-(2-propynyloxy)-4,5-

propynyloxy)mediaminob-cyanopyrimidine \hyleneaminol-maleonilrile 3 I -Amino2 2-Cycloperopylmethoxy4,5

|amino(cyclopropylmelhoxdiamino-o-cyanopyrimidine y )methyleneaminolmaleonitrile 4 l-Amino-Z- 2-Benzyloxy-4.5-diamino'6- (aminobenzyloxymecyanopyrimidine thyleneamino)maleonitrile 5 lAmino-Z 2-Ethoxymethoxy-4.5-

I uminoi ethoxymethoxy diamino-6-cyanopyrimidine mcthyleneaminolmaleonitrile o l-Arnino-2-[amino([3- 2-(B-Ethoxyethoxy)-4,5-

ethoxycthoxy )mc diaminoli-cyanopyrimidine thylencaminol-muleonitrile 7 l-Amino-Z- 2-lsopropyloxy-4jdiamino- [aminoisopropyloxyme- 6-cyanopyrimidene thylencamino)maleonitrilc 8 l Amino-ll amino( 3 24 3-Chlorobutoxy )-4.5-

chlorobutoxy lmcdiumino-(rcyanopyrimidine thyleneaminoI-maleonitrile 9 l Amino-2-[amino( 2- 2-( 2 Chloroethoxy )-4.5

chloroethoxy )mediamino-b-cyanopyrimidine thyleneaminol-maleonitrile l0 l'Amino-2-[amino( 2- 2-( 2 Fluoroethoxy )-4,5-

fluoroethoxy)methyleneaminol-maleonitrile l-Amino-Z-I amino( 2- Nitropropoxy)methyleneamino]maleonitrile diamino-flcyanopyrimidine 2-( 2-Nitropropoxy)-4.5- diamino-6 cyanopyrimidine When the cyanoformimidates of Formula I in which R is CH CF CF CH(CFa)z, CH C(NO CH -CH -(CF -H or -CH -CHCl are sub stituted for 2,2,2-trifluoroethyl cyanoformimidate in the procedure of Example 4, Part B, the product in each case is l-amino-2(aminocyanomethyleneamino)- maleonitrile, which is cyclized to 2,6-dicyano-4,5- diaminopyrimidine by the procedure of Example 6.

EXAMPLE A As noted above, the products of Formula III are useful curing agents for epoxy resins, as shown by the following:

Part A A slurry of 0.15 g of 2,6-dicyano-4,5- diaminopyrimidine in 3.0 g of a partly polymerized diglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane (Epon-828 from the Shell Chemical Company) was heated at l50C. After 0.5 hour the resulting solution began to thicken and had darkened in color. After 1 hour the material was rubbery in texture and after l.5 hours at C the product was cured to a glass hard polymer.

Part B A control of Epon-828 without any pyrimidine remained a clear, uncured liquid after 16 hours at l50C.

Part C A slurry of 0.15 g of 2-methoxy-4,5-diamino-6- cyanopyrimidine in 3.0 g of Epon-828 was heated as above. Within 2.5 hours at l50C the product was cured to a glass hard polymer.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A compound of the formula H N-C 9 X is ON or R -C-R .vhere in 2-methoxy-4,5- 

1. A COMPOUND OF THE FORMULA 2-X,4,5-DI(H2N-),6-(NC-)PYRIMIDINE, WHEREIN X IS NC- OR R1-CH(-R2)-O-, R1 AND R2, ALIKE OR DIFFERENT, BEING H OR ALKYL, ALKOXY, ALKENYL, ALKYNYL OF ALKOXYALKYL OF UP TO 7 CARBONS, UNSUBSTITUTED OR SUBSTITUTED WITH UP TO 14 HALOGEN AND/OR NITRO, OR PHENYL, UNSUBSTITUTED OR SUBSTITUTED WITH UP TO 5 HALOGEN AND/OR NITRO, WITH THE PROVISO THAT ANY A-CARBON IN R1 OR R2 CARRIES NO MORE THAN ONE FLUORO, CHLORO OR NITRO SUBSTITUENT.
 2. The compound of claim 1, 2,6-dicyano-4,5-diaminopyrimidine.
 3. The compound of claim 1, 2-methoxy-4,5-diamino-6-cyanopyrimidine.
 4. The compound of claim 1, 2-ethoxy-4,5-diamino-6-cyanopyrimidine. 